Abstract
Abstract In this paper, we develop an early idea of one of the authors (Nuritdinov 1992a,b), who was the first to propose the mechanism of instability of the warp perturbation mode on the background of a nonstationary disk. For this aim, we have studied a model of a nonlinearly non-stationary self-gravitating disk with an anisotropic velocity diagram. The model has a composite nature, or rather, it is a superposition of isotropic and anisotropic states of the disk. In the general case, it is obtained a nonstationary analogue of the dispersion equation of this composite model. We have also investigated the behavior of the domed perturbation mode, the instability of which leads to the formation of a classical bulge in the central region of the disk. In addition, we considered the critical diagrams of the dependence of the virial ratio on the rotation rate of the system for various values of the superposition parameter and the corresponding diagrams for the increments of instability.
Highlights
The central bulges of disk galaxies are very different from each other
In this paper, we develop an early idea of one of the authors (Nuritdinov 1992a,b), who was the first to propose the mechanism of instability of the warp perturbation mode on the background of a nonstationary disk
We have studied a model of a nonlinearly non-stationary self-gravitating disk with an anisotropic velocity diagram
Summary
The central bulges of disk galaxies are very different from each other. We observe large classical bulges of galaxies like the galaxy NGC4594 and vice versa, clearly smaller boxy bulges of later-type disk galaxies, similar to our own Galaxy. Its formation can occur at the nonlinearly non-stationary evolution stage of galaxies, for example, due to the gravitational instability of vertical oscillations of the central region of the disk This idea was proposed by one of the authors of this work (Nuritdinov 1992a,b). Among the various possible non-stationarities of the disk subsystem of galaxies, a special place is occupied by its radial oscillations In reality, they may have not very large amplitudes, but theoretically it is easier to construct radially pulsating disks, generalizing some well-known equilibrium models to this case. Nuritdinov, Nonlinear cosmogony of the spiral galaxy bulges | 145 virial parameter and one can write in the following form as λ = 1 − (︀2T/|U|)︀0,.
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